W. Sapp

A cryogenic tritium target system for nuclear physics experiments

Abstract A cryogenic tritium ( 3 H 2 ) gas target system was constructed and used for a program of electron scattering studies. The 3 H 2 was supplied and safely stored as solid U 3 H 3 . For the experiments, it was transferred to a thin walled cylindrical cell, where it was exposed to 25 μA electron beams with energies up to 800 MeV. During operation, the target cell contained 115000 Ci of tritium at 225 psia and 45 K. Multiple safety enclosures surrounded both target and gas transfer systems. A microprocessor-based control and monitoring system presented target parameters to the operators, identifying those out of range. The target system operated safely and effectively for about 2000 h, enabling completion of comprehensive elastic and elastic electron scattering study of the three nucleon system.

Commissioning the MIT-Bates South Hall Ring

The South Hall Ring at the MIT-Bates Linear Accelerator Center is a 1 GeV electron ring for nuclear physics experiments. It is designed to operate in two modes: as a pulse stretcher to deliver high duty factor beams to external targets, and as a storage ring for internal target experiments. To date we have injected beam into the ring using one and two-turn injection, stored beam with a lifetime of several minutes, and achieved early results performing half-integer resonant extraction from the ring in pulse stretcher mode. Experience in commissioning the ring is presented. Future plans for extraction, improved storage and backgrounds, and spin control and measurement in the ring, are also discussed.

Status of the MIT-Bates South Hall Ring commissioning

This work discusses commissioning of the injection line, the Energy Compression System and the South Hall Ring. Future plans are considered.<<ETX>>

Control of roll in fiducialization of quadrupole magnets for the MIT-Bates South Hall Ring

The South Hall Ring (SHR) requires for all 94 quadrupoles in the lattice a roll tolerance of less than 2 mr. An important step in achieving this tolerance is the fiducialization: the relating of the magnetic axes to the position of the survey targets fixed to the magnet. The fiducialization procedure which we developed involved a harmonic analyzer system and the SLAC Industrial Measurement System. After fiducialization and database generation had been completed for over 1/3 of the elements, and after the precision installation had begun, we noticed a random roll well outside the tolerances. The roll had been overlooked partially because the harmonic analyser system is insensitive to rotations about the coil axis. We were able to overcome the problem through software by developing an extensive algorithm and regenerating the database without a need for refiducialization. This correction process for both the roll and the pitch will be presented.<<ETX>>

Magnetic measurement, fiducialization and alignment of large dipoles for the MIT-Bates SHR

The South Hall Ring (SHR) lattice uses sixteen large dipoles originally designed for the Princeton-Pennsylvania Accelerator. These 3.6 m long, 30 ton dipoles have bend radii of over 9 meters and gaps of only 7.6 cm. The requirement that the four dipoles be powered in series, as well as other restrictions, resulted in magnetic and mechanical alignment tolerances which are very demanding for magnets of this size and shape. Two independent methods were used for measurement of the field integral along the design orbit. Field integrals were measured on all dipoles using a long coil excited by ramping the field. On four dipoles, the integrals were also measured using Hall probes moving along the design orbit. The techniques and results will be presented. The fiducialization of these dipoles was accomplished using precision-machined fixtures and the SLAC computer-aided Industrial Measurement System. Position corrections due to different measured effective lengths of these magnets will be discussed, and details of fiducialization and alignment will be presented.<<ETX>>

Survey and alignment of the MIT-Bates South Hall Ring

The South Hall Ring (SHR) is a pulse storage/stretcher ring with a circumference of 190 m. The complex contains over 200 magnetic elements, most of which must be positioned to tight tolerances to achieve efficient injection and extraction and to obtain storage times of several seconds for internal targets. In particular, the lattice quadrupoles have transverse position tolerances of /spl plusmn/100 microns magnet-to-magnet, and the circumference has a tolerance of /spl plusmn/5 mm. For the survey and alignment of the ring, we have used automated data capture, data flow and database generation. Alignment of all magnets to approximately /spl plusmn/1/4 mm has been completed. The final survey followed by a smoothing of the lattice will begin soon. The present status and issues of the survey and alignment program will be presented, along with the latest alignment aspects of the beam test results.<<ETX>>

Trinucleon Threshold Electrodisintegration

Inclusive inelastic electron scattering cross sections for 3H and 3He were measured for excitation energies below 18 MeV. For six values of the three-momentum transfer q in the range 0.88 < q < 2.87 fm−1, longitudinal and transverse response functions were determined. The experimental data are in good agreement with two recent calculations. One uses variational ground-state wave functions and the orthogonal correlated states method to describe the two- and three-body breakup channels. The other uses bound and continuum Faddeev wave functions for a simple central potential. The inclusion of final-state interactions (FSI) in the Faddeev continuum is found to be very important; inclusion of FSI changes the response functions in the threshold kinematics by a large amount, yielding excellent agreement with the data.

Magnetic measurement of quadrupole and sextupole magnets for the MIT-Bates South Hall Ring (SHR)

Final results of magnetic measurements of 128 quadrupoles and 32 sextupoles are presented. There are many places in the SHR complex where these magnets will be operated from a common power supply. For the quadrupole magnets there are 4 octets, 4 triplets and 18 doublets; these magnets have been matched to /spl plusmn/0.1% in excitation response for the operating range corresponding to 0.3-1.0 GeV. For the sextupoles there are four octets where the (pairwise) matching has generally been made to the /spl plusmn/0.3% level. Parameterization of the data as well as fits are described and examples of the magnet groupings are shown.<<ETX>>

Measurement of 16O(γ,n0) at medium energies

Exclusive differential (γ,n) cross‐sections on 16O have been measured at Eγ=150, 200 and 250 MeV for θL=50°, 60° and 90°. This measurement is the first of its type to be reported for the energy region above the pion production threshold. Calculations of the (γ,n) reaction indicate that large effects are expected from meson exchange currents. The (γ,n) data will be compared with the predictions of such calculations and with available (γ,p) data.